The goal of this proposal is to study the metabolism and function of neutrophils. We have shown that human neutrophils oxidize methionine to methionine sulfoxide and that this oxidation is dependent on the myeloperoxidase (MPO) system. We propose to study 1) the oxidation and inactivation of methionine enkephalin by human neutrophils and the MPO system, 2) the role of methionine oxidation in the MPO-mediated bacterial killing, 3) the peroxidation of lipid by the MPO system and human neutrophils, and 4) the metabolism and function of neutrophils from patients with suspected neutrophil dysfunction.